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help / color / mirror / Atom feedFrom: Laurenz Albe <[email protected]>
To: Charles Qi <[email protected]>
To: Adrian Klaver <[email protected]>
Cc: [email protected]
Subject: Re: When UPDATE a row in a table with BEFORE ROW UPDATE trigger, the XMAX of new tuple is set to current XID
Date: Sun, 10 Aug 2025 21:34:19 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAEawgcLdD3-4Co8mrR7UaXJLGgBwSecUs-1QxyY3VoJzN9bnmg@mail.gmail.com>
References: <CAEawgcJN2V0MTzZu5gi=csNapnJzogxJJqUFSphu6r=OXjorng@mail.gmail.com>
<[email protected]>
<CAEawgcLdD3-4Co8mrR7UaXJLGgBwSecUs-1QxyY3VoJzN9bnmg@mail.gmail.com>
On Fri, 2025-08-08 at 09:20 +0800, Charles Qi wrote:
> Let me clarify the question, when the BEFORE ROW UPDATE trigger is presented
> Q. Why do we need to set the XMAX of the new tuple to the current xid?
Because the row gets locked, I'd say (without looking at your example).
> which risks piling up multixacts quickly in savepoint/exception block
> scenarios.
Why is that a problem for you?
Perhaps the trigger could use SELECT ... FOR ... to lock the row in the
strongest level your transaction needs. A multixact is only necessary
if a subtransaction needs to take a stronger lock on the row than what
was there before.
Yours,
Laurenz Albe
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Subject: Re: When UPDATE a row in a table with BEFORE ROW UPDATE trigger, the XMAX of new tuple is set to current XID
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